I had some of the same problems with Exchange since the 2.1 OTA. I'd set it to sync "as they arrive" but when I looked later it was set at "every 15 minutes". The notification sound also seemed to turn itself off so I would get messages but not hear them arrive. Very frustrating because it worked pretty well on 1.5.

Gmail by-the-way, has always worked well.

Bottom line: I did a factory reset, checked/made all of the Exchange settings, and the Eris seems to be behaving now.

Word is that Exchange integration is going to be much better on Froyo (2.2) but sadly, I doubt Eris owners will see this officially supported by Verizon and arrive OTA.

I think a factory reset is in your future too. I did one and all my settings are holding.

Although, I am having issues not receiving my exchange email unless I am on 3G after the 2.1 OTA. I have it set to notify as items arrive. I live and work in two different cities. While at work, I am on Verizon's network (3G). While at home, I am on an Extended network (1x). Everything works fine at work, but when I am at home, I have to manually refresh to receive my work emails. It did not do this on 1.5. If I go into the Exchange ActiveSync options, there is an option to Sync when Roaming, but it is greyed out and I can't check it.